Bump rack from 2.0.7 to 2.0.8 in /examples/simple_rails_api

Bumps [rack](https://github.com/rack/rack) from 2.0.7 to 2.0.8.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](rack/rack@2.0.7...2.0.8)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

examples/simple_rails_api/Gemfile.lock

@@ -90,7 +90,7 @@ GEM
       mini_portile2 (~> 2.4.0)
     puma (4.3.1)
       nio4r (~> 2.0)
-    rack (2.0.7)
+    rack (2.0.8)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rails (6.0.2)